4.0 running rich

my 89 xj 4.0 has been running rough and stalls intermittently. I replaced the fuel pump and it ran well for about 10 miles and started doing the same things, rough idle, backfires. I had the local muffler shop put a new muffler in it a month ago and replaced it today, telling me they wouldn't do it again because the backfire had caused it to burn out. they further told me it was running very rich (which i could tell by the smell). it's been tuned, new plugs, rotor, cap etc. I am thinking it's the 02 sensor, though it didn't come up on the computer. 95000 miles on it. i am going to go ahead and replace it. any thoughts on this? it gets very bad mileage as well. anyone have a link to pictures of the o2 sensor location?

thanks

davehoose

correct me if i am wrong but i didnt think the renix system had a dtc , so u have no check engine light , usually you check all your sensor with a multimeter , but i would check your tps i know mine was back firing out of the tb and that was why my tps was out of adjustment .

It could very well be the O2 sensor, judging by the behavior. Not sure where located on a pre-HO motor, but most are located in the exhaust downpipe on the driver's side, just about the same level as the oil pan drain plug, real close to the pan, can't miss it.

Try unplugging the O2 sensor first. If the Jeep runs perfectly without the sensor (i.e. no backfiring), then it must be the O2 sensor causing the problem. It will still run rich with the O2 sensor unplugged, btw, so you'll need to replace the sensor at some point. HTH